firegnu

function sharpen(ctx, w, h, mix) {
    var x, sx, sy, r, g, b, a, dstOff, srcOff, wt, cx, cy, scy, scx,
        weights = [0, -1, 0, -1, 5, -1, 0, -1, 0],
        katet = Math.round(Math.sqrt(weights.length)),
        half = (katet * 0.5) | 0,
        dstData = ctx.createImageData(w, h),
        dstBuff = dstData.data,
        srcBuff = ctx.getImageData(0, 0, w, h).data,
        y = h;

firegnu

/build